The invention relates to a method and apparatus for recognizing malfunctions of a vehicular heater operated with liquid fuel, the heater having assigned to it a control unit for control of the operating cycles, as well as a display for indication of the operating state of the heater. The display is supplied with the output signal of a function testing circuit with which all functions essential to the operation are polled successively and determined by a comparison between desired and actual values of electrical voltages associated with the functions by means of a polling control.
The term "heater" is meant to include not only the heating equipment provided for heating the interior of a vehicle, but also e.g. cooking stoves in trailers or campers. The fuel used may be liquid propane, heating gas, or other fuel. The vehicles also include boats or building site equipment such as Caterpillar (a trademark) vehicles or cranes, in which engine-independent heaters are installed.
Engine independent heaters for vehicles are known whose current supply is through a battery belonging to the vehicle. These heaters have a control unit for control of their operational cycle. A display means associated with the heater indicates, by lighting up, the switch setting of the heater as soon as the latter is turned on. The function of the control unit is to control the timing according to a given pattern. In particular the blower motor, the fuel feed and the ignition are controlled so that safe operation is possible. At the same time the heater components are monitored as to their functioning and timing. In case of irregularities and malfunctions, the heater is stopped permanently. The cause for stopping the heater remains stored in the control unit until the heater is disconnected.
In known heaters, testing the functions of the individual components is possible only by testing each component individually, including the control unit. Much effort is necessary for this and at least involves locating a customer service shop.
Checking by the user himself is not possible with known heaters. This makes it impossible for the user to fix minor defects himself, and also the shop must first make a relatively expensive diagnosis to identify the trouble spot.
Further a diagnostic system is known which permits defect representation by means of the tachometer and a control bulb. The diagnosis is initiated through the establishment of a state on sensors which normally does not occur during travel. If, with the ignition on, the full load and no load switches are actuated simultaneously, the diagnostic process begins. Occurring defects are shown on the display one after the other, operation of the brake light switch causing it to advance from one defect display to the next. The mechanic reads the correlation between the defects and the tachometer indication from a table. When all defects have been represented, the indication starts over again with the first. After the ignition is turned off, the diagnostic process ends.